The UN children's agency says 1.4 million children overall are "on the run" in Nigeria and neighbouring countries where the group has sown terror in recent months.

More than half of the 1.2 million children who have fled northern Nigeria are aged under five.

Spokesman Christophe Boulierac says Unicef is in "full operational mode" in the region but has received less than a third of the 50 million dollars (£32 million) funding it has sought for the Lake Chad region.

Speaking at a UN news conference in Geneva, Mr Boulierac also appealed for renewed attention on the 219 girls abducted in April last year from a school in Chibok, Nigeria.